Tuning fork assembly for use with rotary timepiece movement



Dec. 23, I969 KAzuo lsHlKAwA ETAL 3,435,032

TUNING FORK ASSEMBLY FOR USE WITH ROTARY TIMEPIECE MOVEMENT Original Filed June 8,1965 5 Sheets-Sheet 1 I mvsw'roRs KAzuo [sHmAwA BY KOICH! IWAKI WJ Z MAAJJ/J IM A-r TORNEVS v Dec. 23, 196-9 KAZUQ sl-n w ETAL 3,485,032

TUNING FORK ASSEMBLY FOR USE WITH ROTARY TIMEPIECE MOVEMENT Qriginal Filed June 8. 1965 3 Sheets-Sheet 2 mwsmozzs KAZUO ISHIKAWA By KoIcHl IWAKI ATTO R NEYS D c- 23, 1969 KAZUOISHIKAWA ETAL. 3,485,032

TUNING FORK ASSEMBLY FOR USE WITH ROTARY TIMEPIECE MOVEMENT Original Filed June 8' 1965 5 Sheets-Sheet 5 INVENTORS KAzuo I HIKAWA BY KOICHI WAKI ATTORNEYS United States Patent ()fiice 3,485,032 Patented Dec. 23, 1969 US. Cl. 5823 9 Claims ABSTRACT OF THE DISCLOSURE A tuning fork assembly for use with a toothed rotary member, made of a magnetic flux-conducting material, for converting the oscillatory movement of the tuning fork into continuous rotational movement of the rotary member, suitable for use in a rotary timepiece movement. The tuning fork is magnetically coupled to the rotary member by means of one or more C-shaped magnets mounted on the ends of the fork tines so that the teeth of the rotary member pass through the slot of the C.

This application is a continuation of abandoned application Ser. No. 462,346, filed June 8, 1965, which, in turn, is a continuation-in-part of our copending application Ser. No. 230,182, filed Oct. 12, 1962, and entitled Magnetic Escapement and which is now Patent No. 3,208,287.

The present invention relates generally to an improved tuning fork assembly for use in timepieces and, more particularly, to an improved tuning fork assembly for use in controlling the rotational velocity of a rotary timepiece movement of the type including a rotary member forming a circular array of radially extending, circumferentially spaced elements made of a magnetic flux conducting material.

It is a primary object of the present invention to provide an improved tuning fork assembly which permits the use of the tuning fork either as a driving element for a rotary timepiece movement or as a velocity control element in a magnetic escapement mechanism. A related object is to provide such a tuning fork assembly which obviates mechanical coupling between the tuning fork and the rotary member operatively associated therewith.

It is another object of the present invention to provide an improved tuning fork assembly for controlling the rotational velocity of a rotary timepiece movement in which either one or both of the tines of the tuning fork may be magnetically coupled to the rotary member being controlled by the fork.

A further object of this invention is to provide an improved tuning fork assembly of the foregoing type which is relatively simple and economical to manufacture and which permits the tuning fork to be magnetically coupled to the rotary timepiece movement with a minimum of parts.

Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which:

FIGURE 1 is a perspective view of a rotary timepiece movement including a magnetic escapement mechanism utilizing a tuning fork assembly embodying the present invention;

FIG. 2 is a plan view of a modified magnetic escapement mechanism utilizing a tuning fork assembly embodying the present invention;

FIG. 3 is a side elevation of the mechanism of FIG. 2; and 1 FIGS. 4 through 7 are fragmentary plan views of various portions of the rotary member shown in FIGS. 1 through 3 with the double hatched areas representing projections of one pair of magnetic poles carried by the tuning fork.

Turning now to the drawings, in FIGURE 1 there is illustrated a conventional rotary timepiece movement including a plurality of spaced parallel plates 1, 2 and 3 which are held together by a plurality of pins 4, 5, 6 and 7. The rotary movement is driven by a D-C motor 8 via a drive shaft 9. Rotation of the shaft 9 winds a spring 10 which, in turn, drives a rotary disc 11 via a pin 12 which is attached to the rotary disc 11 and projects therefrom into engagement with the free end of the spring 10.

From the rotary disc 11, the rotary motion is transmitted through a gear train, which drives suitable indicating mechanism (not shown), to an escape wheel 25. The gear train is a conventional type and includes a gear 14 mounted on a shaft 13; a gear 15 mounted on a shaft 16; gears 17, 18 and 19 mounted on a shaft 20; gear 28 mounted on a shaft 27; gears 21 and 22 mounted on a shaft 23; and finally a gear.24 mounted on a shaft 26 to drive the escape wheel 25.

The escape wheel 25 is designed to form two concentric sets of radially extending, circumferentially spaced magnetic elements with the elements in one of said sets being circumferentially offset from the elements in the other set. Thus, the wheel 25 includes a plurality of circumferentially spaced radial teeth 25a which are made of a magnetic flux conducting material to form the first set of magnetic elements. Spaced inwardly from the magnetic teeth 25a is a circular array of radial apertures 25b which are aligned with the magnetic teeth 25a so as to form a plurality of radial ribs 250 which form the second set of magnetic elements. It can be seen that the magnetic ribs 25c are arranged concentrically with respect to the magnetic teeth 25a and are circumferentially offset from the magnetic teeth 25a.

In accordance with the present invention, there is provided an improved tuning fork assembly for controlling the rotational velocity of the aforedescribed escape wheel, which tuning fork assembly comprises the combination of a tuning fork including a base portion and a pair of tines adapted to vibrate alternately toward and away from each other at a predetermined natural frequency of vibration, a permanent magnet mounted on one of the tines with the opposite poles of the magnet defining an open slot extending in the direction of vibration of the tines to enable vibratory movement of the magnetic poles radially with respect to the escape wheel with the poles on opposite sides of the escape wheel while permitting rotation of the wheel relative to the fork, and a weight substantially equivalent to the magnet in moment of inertia mounted on the other tine of the fork. Thus, in the illustrative escapement mechanism shown in the drawings, a tuning fork 29 having a base portion 29a and a pair of tines 29b is firmly secured to a rigid mounting block 30 by means of a rod 35. The mounting block 30 is fastened to the plate 1 by means of a plurality of bolts 31. Mounted on the outer end of one of the fork tines 29b is an arcuate or C-shaped permanent magnet with the opposite magnetic poles at the ends of the C defining an open slot. The tuning fork is mounted so that the magnetic elements formed by the escape 'wheel 25 pass through the slot, between the opposed magnetic poles, as the escape wheel is rotated. The C-shaped magnet is mounted perpendicular to the plane of vibration so that the opposed faces of the magnetic poles extend in the direction of vibration of the fork tines so as to enable vibratory movement of the tines relative to the escape wheel while maintaining a substantially constant air gap between the vibrating magnetic poles and the rotating magnetic elements. Thus, the magnetic poles are located on opposite sides of the rotating escape wheel 25 so that the radial magnetic elements formed by the wheel are continuously pasing through the magnetic field created by the opposed poles.

For the purpose of balancing the tuning fork, a C-shaped weight 33 is mounted on the other fork tine. The weight 33 is of the same size, shape and mass as the magnetic member 32 so that the elements mounted on the two tines are substantially equivalent to each other in moment of inertia.

In order to avoid any cantilever type oscillation of the tuning fork 29, it is preferred to mount magnets on both of the fork tines so that both tines may be magnetically coupled to the escape wheel 25. Thus, in the preferred embodiment illustrated in FIGS. 2 and 3, both of the C-shaped members 32 and 33 are permanent magnets and the escape wheel is disposed between the opposed pole faces of both magnets so as to be magnetically coupled to the tuning fork at two spaced points which are symmetrically located relative to the tuning fork. This arrangement tends to equalize the load on the two tines and thereby avoid any cantilever type oscillatory motion of the tuning fork.

As the escape wheel 25 is driven by the motor 8 and associated gear train, it initiates vibratory motion of the tuning fork 29 at approximately the natural frequency of vibration of the tuning fork. Although the amplitude of the oscillatory movement of the tuning fork may vary somewhat with fluctuations in the rotational speed of the escape wheel 25, the tuning fork will continue to vibrate at a substantially constant frequency as long as the escape wheel 25 continues to rotate. Since the tuning fork 29 vibrates at a substantially constant frequency, and since it is magnetically coupled to the rotating escape wheel, the tuning fork functions to correct any fluctuations in the rotational speed of the escape wheel 25 so as to maintain the escape wheel and thus the rotary timepiece movement at a substantially constant speed.

For a more detailed explanation of the magnetic coupling between the tuning fork and the escape wheel and an understanding of how this magnetic coupling controls the rotational speed of the escape wheel, reference is now made to FIGS. 4 and 5. Assuming that the tuning fork is already vibrating and that the escape wheel 25 is rotating in the clockwise direction, it can be seen that the faces of the opposed poles of the C-shaped magnet will vibrate' radially back and forth across the magnetic elements 25a and 25c passing therebetween. One instantaneous position of the magnetic poles relative to the wheel 25 is indicated by the double hatched area in FIGS. 4 and 5. The tuning fork vibrates at a constant frequency so that the magnetic poles will always vibrate through the same number of cycles for any given time interval, irrespective of any fluctuations in the amplitude of the vibratory motion of the tuning fork.

When the escape wheel 25 is driven at a rotational velocity which is exactly synchronized with the frequency of the vibratory motion of the tuning fork, the magnetic poles will move into exact alignment with the center line of one of the magnetic teeth 25a during the outer excursion of each vibratory cycle of the tuning fork. Similarly, during the inward excursion of each vibratory cycle, the magnetic poles will move into alignment with the center line of one of the magnetic ribs 250. As can be seen in FIGS. 4 and 5, the magnetic poles will be symmetrical with respect to the magnetic elements 25a and 250 during such synchronized movement, so that the net torque on the escape wheel 25 is essentially zero.

When the escape wheel moves ahead of the constant frequency tuning fork, the magnetic poles will lag slightly behind the center lines of the m gnetic elements 25a and 250, as illustrated in FIGS. 6 and 7. This produces an asymmetrical relationship between the magnetic poles and the radially extending magnetic elements 251: and 25c, with the resultant magnetic forces producing a slight counterclockwise torque or drag on the rotating escape wheel. This tends to reduce the speed of the escape wheel until it is again synchronized with the vibratory motion of the tuning fork.

Conversely, if the rotational velocity of the escape wheel 25 is reduced so that it falls behind the constant frequency vibration of the tuning fork tines, the magnetic poles will move slightly ahead of the center lines of the radial magnetic elements. The resultant magnetic forces will then exert a slight clockwise or accelerating torque on the escape wheel until it is again synchronized with the vibratory motion of the tuning fork.

The vibratory motion of the tuning fork is sustained by the driving impulses applied thereto by the magnetic coupling between the opposed magnetic poles and the radial magnetic elements on the escape wheel. Although the magnitude of these driving impulses may vary somewhat with the fluctuations in the speed of the escape wheel before such fluctuations can be corrected, this affects only the amplitude of the fork vibration and the frequency thereof remains constant. Thus, it can be seen that the tuning fork provides an automatic velocity regulator for the escape Wheel 25, and this regulation is completely independent of the amplitude of the vibratory movement of the tuning fork tines.

Although the invention has been described with particular reference to its use in a magnetic escapement mechanism, it should be recognized that the tuning fork assembly provided by this invention has numerous other applications. For example, the inventive tuning fork assembly can be used as a constant frequency driving means for a rotary timepiece movement; that is, the driving force is applied to the tuning fork rather than to the rotary timepiece movement, and the tuning fork then transmits the driving force to a rotary member having the same configuration as the magnetic escape wheel described above. The rotary member, in turn, is mechanically coupled to the rotary timepiece movement for the purpose of driving the same. An example of this type of mechanism utilizing the tuning fork assembly of this invention is described in more detail in copending applcaton Ser. No. 291,763, filed July 1, 1963, entitled Tuning Fork Clock, which is assigned to the assignee of the present application.

It is to be understood that the term tuning fork as used herein is not limited to any particular type of tuning fork. For example, although the invention has been described with particular reference to a conventional U-shaped tuning fork having substantially linear tines, the. invention is equally applicable to circular tuning forks or any other fork configuration.

We claim as our invention:

'1. A tuning fork assembly for controlling the velocity of a rotary timepiece movement, a tuning fork including a base portion and a pair of tines adapted to vibrate alternately toward and away from each other at a predetermined natural frequency of vibration, a permanent magnet mounted on one of said tines with the opposite poles of the magnet defining an open slot extending in the direction of vibration of said tines so as to enable vibratory movement of said poles with a substantially constant air gap between said magnetic poles, and a weight substantially equivalent to said magnet in moment of inertia mounted on the other of said tines.

2. A tuning fork assembly for controlling the velocity of a rotary timepiece movement, said tuning fork assembly comprising the combination of a tuning fork including a base portion and a pair of tines adapted to vibrate alternately toward and away from each other at a predetermined natural frequency of vibration, an arcu-. ate magnet mounted on one of said tines with the mag netic poles at opposite ends of the arc defining an open slot extending in the direction of vibration of said tines so as to enable vibratory movement of said magnetic poles with a substantially constant air gap between said magnetic poles, and a weight substantially equivalent to said magnet in moment of inertia mounted on the other of said tines.

3. A tuning fork assembly for controlling the rotational velocity of a rotary timepiece movement, said tuning fork assembly comprising the combination of a tuning fork including a base portion and a pair of tines adapted to vibrate alternately toward and away from each other at a predetermined natural frequency of vibration, a substantially C-shaped magnet mounted on one of said tine-s with opposite magnetic poles at the ends of the C forming a slot extending in the direction of vibration of said tines to enable vibratory movement of said magnetic poles with a substantially constant air gap between said magnetic poles and a weight substantially equivalent to said magnet in movement of inertia mounted on the other of said tines.

4. A tuning fork assembly for controlling the rotational velocity of a rotary timepiece movement, said tuning fork assembly comprising the combination of a tuning fork including a base portion and a pair of tines adapted to vibrate alternately toward and away from each other at a predetermined natural frequency of vibration, a permanent magnet mounted on one of said tines, said permanent magnet including a pair of opposed substantially parallel surfaces extending in the same direction as the vibratory motion of said tines so as to form an air gap which is open in the direction of said vibratory movement, the opposite magnetic poles of said magnet being formed on said opposed surfaces so as to create a magnetic field extending through said air gap in a direction substantially normal to the direction of said vibratory movement, and a weight substantially equivalent to said magnet in mo ment of inertia mounted on the other of said tines.

5. A tuning fork assembly for controlling the rotational velocity of a rotary timepiece movement, said tuning fork assembly comprising the combination of a tuning fork inculding a base portion and a pair of tines adapted to vibrate alternately toward and away from each other at a predetermined natural frequency of vibration, a per manent magnet mounted on one of said tines and comprising a split annulus with the split forming two opposed end surfaces with the opposite poles of the magnet being located at said opposed end surfaces so as to create a magnetic field in the air gap between said surfaces, said air gap being open in the direction of vibration of said tines so as to enable vibratory movement of said poles with a substantially constant air gap between said mag netic poles, and a weight substantially equivalent to said magnet in moment of inertia mounted on the other of said tines.

6. A tuning fork assembly suitable for use in controlling the rotational velocity of a rotary timepiece movement, said tuning fork assembly comprising the combination of a tuning fork, including a base portion and a pair of tines adapted to vibrate alternately toward and away from each other at a predetermined natural frequency of vibration, a pair of permanent magnets one of which is mounted on one of said tines and the other of which is mounted on the other of said tines, said magnets being symmetrically located with respect to each other and with respect to said fork with the opposite poles of each magnet defining an open slot extending in the direction of vibration of said tines so as to enable vibratory movement of said poles with a substantially constant air gap between said magnetic poles, and a weight substantially equivalent to said magnet in moment of inertia mounted on the other of said tines.

7. A tuning fork assembly for controlling the rotational velocity of a rotary timepiece movement, said tuning fork assembly comprising the combination of a tuning fork including a base portion and a pair of tines adapted to vibrate alternately toward and away from each other at a predetermined natural frequency of vibration, a pair of substantially C-shaped permanent magnets one of which is mounted on one of said tines and the other of which is mounted on the other of said tines, said magnets being symmetrically located with respect to said tuning fork with the opposite magnetic poles of each magnet being located at the ends of the C so as to define an open slot extending in the direction of vibration of said tines to enable vibratory movement of said magnetic poles with a substantially constant air gap between said magnetic po es.

8. A tuning fork assembly for controlling the velocity of a rotary timepiece movement, said tuning fork assembly comprising the combination of a tuning fork including a base portion and a pair of tines adapted to vibrate alternately toward and away from each other at a predetermined natural frequency of vibration, a pair of armate permanent magnets one of which is mounted on one of said tines and the other of which is mounted on the other of said tines, said magnets being symmetrically located with respect to said tuning fork with the opposite magnetic poles of each magnet defining an open slot extending in the direction of vibration of said tines so as to enable vibratory movement of said magnetic poles with a substantially constant air gap between said magnetic poles.

9. A tuning fork assembly suitable for use in controlling the rotational velocity of a rotary timepiece movement, said tuning fork assembly comprising the combina tion of a tuning fork including a base portion and a pair of tines adapted to vibrate alternately toward and away from each other at a predetermined natural frequency of vibration, a pair of permanent magnets one of which is mounted on one of said tines and the other of which is mounted on the other of said tines, each of said permanent magnets including a pair of opposed pole faces of opposite polarity and extending in the same direction as the vibratory motion of said tines so as to form an air gap which is open in the direction of said vibratory motion, with the opposite magnetic poles of each magnet creating a magnetic field extending through said air gap in a direction substantially normal to the direction of said vibratory motion, said magnets being symmetrically located with respect to said tuning fork.

References Cited UNITED STATES PATENTS 3,208,287 9/1965 Ishikawa et a1. 58-116 FOREIGN PATENTS 660,581 Great Britain.

RICHARD B. WILKINSON, Primary Examiner E. C. SIMMONS, Assistant Examiner U.S. Cl. X.R. 58-l16 

